The technique consisting in communicating a false twist to a yarn by friction has been known for a long time. This technique generally consists in placing the moving yarn in contact with a mobile surface, moving transversely with respect to the path of said yarn, so that the latter is twisted upstream and resumes its initial twist downstream.
This technique, for which numerous applications have been envisaged, has been especially used up to the present time for texturing synthetic yarns, i.e. for communicating thereto voluminosity and elasticity by a heat treatment followed by a cooling of the yarn upstream of the false twist member.
Various other applications of false twist have also been envisaged, particularly for making fancy yarns, yarns presenting alternate twists over their length, self-twisted yarns, simple or complex spun yarns of fibers, for example comprising an internal core.
Numerous solutions have been proposed for the mobile surface for communicating a twist to a yarn by friction. Those used up to the present time in the domain of texturing employ either bushings against the surface of which the yarn is in contact (false twist by internal friction) or overlapping discs mounted on parallel spindles, the moving yarn coming into contact with the outer surface of said discs (false twist by external friction).
It has long since been proposed, particularly in French Pat. Nos. 1,191,361, and 1,255,922, and in U.S. Pat. No. 2,908,133, to constitute the member for communicating the false twist by one or more endless belts or aprons against the surface of which the yarn rubs.
It has also been proposed, as disclosed in U.S. Pat. No. 2,262,589 and French Pat. No. 1,076,599, to communicate a false twist by passing the yarn, whether it is based on continuous filaments or on discontinuous fibers, between two mobile aprons, these aprons being disposed obliquely with respect to each other so that the yarn is given a certain impulsion in the direction of its displacement during passage thereof between the aprons. The invention relates to an improvement to this latter type of false twist device.
Such a device incorporating aprons will be referred to in the following specification as an "angled apron spindle".
Among the problems raised for such angled apron spindles and which are a function of the material treated, the speed of production, the rate of twist which it is desired to communicate, mention may be made of those of the inclination of one apron with respect to the other, of the pressure of said aprons against each other, and/or of the tension of each of the aprons.
Furthermore, such spindles must be able to allow easy positioning of the yarn at start-up, must offer the possibility of regulating the speed of advance of the aprons and must enable said aprons to be easily changed when they are worn out.
Taken separately, each of these problems can be solved without difficulty by the man skilled in the art.
On the other hand, no solution has yet been proposed for solving them simultaneously.
Moreover, in all the devices proposed up to the present time, there is the problem of maintaining the aprons in position around their support rollers, being given that, in normal operation, said aprons under the action of the stresses exerted by the passage of the yarn tend to move transversely, which disturbs correct operation. At the present time, in the textile domain, in order to hold the aprons around the drive rollers, for example in the spindles or even in the yarn delivering members, the solutions proposed have consisted either in providing rollers whose width is less than the width of the aprons, or in using convex rollers.
Finally, at the present time, in such angled aprons, it is necessary to have rollers presenting a relatively large diameter, which rollers are always of equal diameters, which results in increasing the space requirement of such spindles and especially in removing the twisting member from the means which deliver the material (yarn or fiber) to be treated.
An improvement to such types of angled apron spindles has now been found, and this forms the subject matter of the present invention, improvement which is particularly simple, easy to use and maintain, of small dimensions, which not only enables the above-mentioned adjustments (inclination of the aprons, pressure therebetween, . . . ) to be easily obtained, but also eliminates any risk of slide of the aprons with respect to the support rollers.